The Evolution of 2-Stroke Dirt Bikes Over 40 Years: Have There Been Any?

Sometimes it feels like the 2-stroke is older than time itself. They have been around forever, and to this day they still more or less sound and feel about the same as they did in the ‘70s and ‘80s. They sound about the same, they look about the same (big, fat pipes), and they still produce intense thrust-to-weight. In fact, this is exactly why they have been the mainstay of tiny homebuilt airplanes also since the ‘70s and ‘80s (Rotax 2-strokes are the most popular in the world for ultralight airplanes).

Also, 2-strokes reign supreme on jet skis, and a lot of sleds still use them; the high torque and light weight are great for sleds. But what about 2-strokers has actually advanced at all over these past four decades? And where would they be if they had been improved? 

Let’s hash it out. 

Advancements in Power and Speed

Well, first off, it is unfair to say that 2-strokes haven’t improved over the years because they certainly have. 

If anything, the sheer volume of 2 stroke engines has only increased. There are more sleds on the snow, more jet skis on the water, and more dirt bikes on the trails. Of course, the limiting factor is largely that 4 stroke engines have replaced the 2 stroke engine in a lot of applications. 

But a 4 stroke engine, while generally a lot better on fuel economy, noise, and emissions, has drawbacks for these applications. All of the applications where a 2 stroke engine is common have a common thread: weight is a major factor. More specifically, power-to-weight. 

Take a dirt bike: the optimal configuration is to build it as light as possible, with a ton of torque and quick throttle response. A 4 stroke engine weighs, on average, about 20%-30% more than a 2 stroke engine with similar displacement. 

Ultralight aircraft almost exclusively use 2 stroke engines for this exact reason, and now with powered paragliders becoming very popular, 2 stroke engines are more alive than ever. But the real question here is whether technology is improving with demand.    

Two-Stroke Engine Technology Upgrades

The benefits of a 2 stroke engine will probably never be fully replaced by 4 stroke engines, so there will always be a niche for 2 strokers. 

The most noteworthy improvements have predictably been in the areas of fuel delivery and ignition systems, which have arguably been the areas of most significant improvement for all internal combustion engines. 

One of the coolest things about a 2 stroke engine is that they can easily utilize lower grades of gasoline by design. This is definitely a point that is not lost on the dirt bike community. The downside of this is that they lack the mobility of a 4 stroke engine due to their lubrication requirements. 

This is not going to change with 2 stroke engines, but with automatic oilers becoming commonplace and much more reliable than they used to be, by and large, this is still the weakest link for 2 stroke engines. Fuel economy has been another major problem, but we are starting to see significant research into how a 2 stroke engine might hold the key to better fuel efficiency than a 4 stroke engine. 

Suspension and Frame Improvements

Metal technology is the unsung hero of manufacturing technology. Over the course of 40 or 50 years, metal technology has improved. The processes become cleaner with a lot less waste, the alloys stronger and lighter.  

Aluminum has supplanted steel in quite a few bikes because

• It is much lighter than steel

• Modern alloys are very strong (not to the extent of steel, but plenty strong for the application)

• Corrosion prevention

One great example is the Yamaha YZ125, a classic dirt biking staple in continuous production since 1974. For the first thirty years of production, the YZ125 used a steel frame construction, but it has switched to aluminum for the past two decades. 

While the weight reduction doesn’t seem all that significant (less than ten pounds), every pound counts in the game of single-cylinder 2-stroke engines. 

The early, first generation dirt bikes were essentially street bikes with knobby tires; a far cry from today’s purpose-built machines. It is impossible to point to one single advancement. Like all things, these have evolved over decades now. They are the culmination of decades of small improvements to make a modern machine that starts much easier, produces more torque, uses less fuel, and has much more suspension travel. 

Every year brings about some improvements, whether it be in terms of minor adjustments to carburation, suspension, fuel/air mixing, or ignition updates (electronic ignition was the most significant advancement in small engines over their entire historical arc, in my opinion). But overall, a YZ125 is still more or less a YZ125: it is a small, single-cylinder 2 stroke engine stuffed on the lightest frame possible.   

Environmental Considerations

2 stroke dirt bikes have long been known for their BRRRAAAPPPPPSSS and of course, for their copious smog. The 2 stroke engines of yesteryear were notorious smokers. 

Now, here’s the thing: dirt bikes of all varieties are absolutely paltry in number compared to standard automobiles and commercial trucks. In fact, we talked about this at length in our article about the red sticker law in California, which changed dramatically in 2022. 

California alone has nearly 15 million registered automobiles, and it is not likely that the amount of 2 stroke dirt bikes is all that close to that number, nor are those 2 strokers stuck in bumper-to-bumper traffic for three hours a day. Unfortunately, it is hard to find exact figures for these things because OHVs aren’t recorded by DMVs since they aren’t street-legal machines (yet). 

But back to the topic at hand: dirty old 2 stroke engines. 

This is becoming more and more of a misnomer. Fuel quality and quality control is better than five decades ago. Ignition systems are radically better now than any previous time in dirt bike history. What a cool way to think about it: every model year from now moving forward will have better technology than the last, even if it is a small improvement. 

Consider how much improved electrical systems (the average, not specific cases) are than even two decades ago? And just reliability in general? Sure, it’s easy for old timers to point to a small-block Chevy from five decades ago and say: “See? Now that is a simple vehicle.” Yes, it is a simple vehicle. But which one would you really say is more reliable between that and a late-model vehicle? All vehicles have become more reliable with advances in tech. That is an empirical fact. 

Emissions are such a hot button issue, and it has been for decades now. Powersports manufacturers have to take this into consideration, but there are some limitations due wholly to how a 2 stroke engine operates. The best way to clean up a 2 stroke engine is through the fuel/air mixture burn. Since it has a much faster operation, a lot of the fuel/air mixture goes out the pipe in the form of emissions. 

The best way to tackle this is by constantly refining and tuning the ignition process. Better ignition systems always mean a more complete burn, whether it’s a 4-stroke or a 2-stroke engine.   

What's Next for 2-Stroke Dirt Bikes?

A lot of the systems are already in place to optimize 2 stroke engines to their fullest potential. Fuel injection is the first step, and it is used widely on most (if not all) new motorcycles in production. Using a computerized engine management system which takes inputs from O² sensors and other sensors in the system to optimize the fuel-air mixture is the best way to ensure the optimal mixture of fuel and air for the best burn. More accurate and hotter ignition systems are an integral part of this equation as well

Unfortunately, no matter how much more reliable, fuel-efficient, and clean 2 stroke dirt bikes get, they are already heavily controlled in several states (sadly, these are usually the best states to wheel in). 

So, what does the future hold for 2 stroke dirt bikes? 

They still maintain a cult following of diehards and are a mainstay of racing. The modern 2-stroke engine does things that a 4-stroke can only dream of: unmatched throttle response and torque to weight that a 4-stroke will never touch. And let’s be honest: when you’re riding the local trails and tearing up the local Motocross park (find one here), is fuel economy really your top consideration?

No. 

Catching massive air is your main focus. 

Anything Else?

Here at Dirt Legal, we see no reason why your bike shouldn’t be able to pull double duty if you want it to. What do we mean? Well, if you want to drive a 2 stroke dirt bike on public roads, why shouldn’t you? And no, we aren’t talking about hooning it. 

We can get your dirt bike titled and registered in a state that condones such common sense activities. When you partner with us, you will get

• A completely legitimate, street-legal title

• Registration

• A license plate

Once you have these in hand, you are good to go anywhere you like. Of course, you need to abide by DOT lighting rules, mirrors, and you’ll want to slap some DOT street legal tires on there. While your paperwork is all perfectly legal, there is no need to explain the whole thing to Johnny Law during a traffic stop that could have been prevented. 

If you’re ready to take this step, smash the link. Gather up your paperwork, fill out what we send you, and we’ll take care of the rest. In a few weeks, you will get your title, registration, and license plate in the mail. 

Meanwhile, keep enjoying your 2 strokes. They’re fun, they’re loud, and they’re waiting for you to open that throttle wide.